The present invention relates in general to abrading, polishing and erasing tools designed for delivering or blasting a pulverulent, granular or other finely divided solid material entrained in a air stream against a surface that is to be abraded, polished, or erased. The dental industry and other fields, often require a small reliable sandblaster that is hand operated and has a slim nozzle and handpiece assembly. The slim nozzle and handpiece assembly is especially important so that sandblasting may be done in a confined opening. In the dental industry it is necessary to sandblast in the confinement of a patients mouth in order to prepare tooth structures and inplace crowns for a variety of repair and cementing procedures. It is also highly desirable for the sandblaster to be self-contained in order that separate sandblaster components and reservoirs are not needed as it is cumbersome in a dental operatory.
Conventional devices for abrading, polishing and erasing surfaces have a nozzle which is manipulated by hand and an orifice operating to discharge a jet or stream containing a mixture of small solid particles and compressed air. Conventional apparatus further comprise a stationary source of compressed air and pulverulent material. Instruments of these type are shown in the U.S. Patent issued to Paasche, U.S. Pat. No. 2,441,441, showing an erasing tool; also shown in the U.S. Patent to Kurowski, U.S. Pat. No. 4,090,334 is an erasing tool with a remote pulverulent supply reservoir. The Caron U.S. Pat. No. 3,163,963 shows a blaster device wherein the abrasive material is contained in a canister mounted on the blaster handle.
A drawback of the above outlined apparatus is that the source of pulverulent material is separate from the apparatus resulting in inconvenient operation. Other existing devices have a movable supply of pulverulent material but the location of the supply near the nozzle tip prevents the user from working within a confined space. A drawback of other existing apparatus is their need for a pressurized air supply within the pulverulent material supply canister; to avoid moisture build up these pressurized systems require a dehydrated source of compressed air. Other devices use a mechanical valve to control the pulverulent material flow, this however can result in excessive clogging if moisture enters the system; additionally cleaning of a mechanical valve system is time consuming requiring disassembly of the apparatus. Other apparatus that use a gravity feed system tend to provide an unreliable supply of abrading material and require constant adjustments to the supply valve. Some of the newer inventions have attempted to overcome drawbacks of earlier designs but have however resulted in costly complicated designs.